1. Field of the Invention
The present invention relates to a complementary photovoltaic cell that provides both positive and negative voltage sources on the same chip.
2. Description of the Prior Art
For certain applications, it is necessary to provide light-responsive signals of both positive and negative polarity. In the past, this has required the use of two separate devices fabricated on separate semiconductor chips. Physical assembly is difficult, particularly where both photosensors must be exposed to a beam of light of narrow cross-section. A principal object of the present invention is to provide a complementary photovoltaic cell that provides both positive and negative voltage outputs from a device fabricated on a single chip. The complementary junctions are very close to each other on the substrate, so that they can be activated by a narrow beam of light.
Another object of the present invention is to provide a complementary cell in which a higher open circuit voltage is obtained from one of the complementary junctions.
Another object of the present invention is to provide a complementary photovoltaic device in which both the positive and negative outputs can be used as current sources. This is important since in prior art complementary photo-responsive arrangements, the diode of one polarity often provided significantly more current output than the photovoltaic device providing the opposite polarity output. In the present invention, a third, vertical junction supplements the current output from the complementary diode which itself has lesser current output. Use of a vertical junction diode also improves the efficiency of the cell since it exhibits a higher response to light at the long wavelength (red) end of the spectrum.
Another object of the present invention is to provide a photoresponsive device having complementary outputs of opposite polarity in which all of the electrical contacts are accessible on a common surface of the device. This arrangement not only simplifies the connection to an external utilization means, but also permits serial or parallel interconnection of plural devices on the same chip by means of electrical conductors deposited onto the device surface in the final stages of fabrication. By merely changing the final metallurgy mask, any desired interconnection of the devices can be achieved.